Conventional thin-film devices such as insulated-gate FETs use a thin semiconductor film of silicon as an active layer. This layer is about 1500 Å thick. Therefore, where electrodes should be formed on this thin semiconductor film, satisfactory contacts can be made by bringing a metal such as aluminum into direct and intimate contact with the film, in the same way as in the prior art IC fabrication techniques. In these contacts, a silicide such as aluminum silicide is usually formed by a chemical reaction between the aluminum and the semiconductor component such as silicon. Since the semiconductor layer is sufficiently thicker than the silicide layer, no problems take place.
However, researches conducted recently have demonstrated that if the thickness of the active layer is decreased below 1500 Å, for example, between about 100 to 750 Å, then the characteristics of the TFTs are improved. Where electrodes should be formed on such a thin semiconductor layer, or an active layer, it has not been possible to make good contacts by the prior art techniques, because the thickness of the silicide layer grows almost up to the thickness of the semiconductor layer, thus severely deteriorating the electrical characteristics of the contacts. When a stress such as a voltage is kept applied to the contacts for a long time, the contacts deteriorate seriously.
In order to improve the characteristics of the TFTs, thermal treatment effected below 400° C., typically 200-350° C., within hydrogen ambient is needed after formation of the electrodes on the semiconductor layer. Where the thickness of the semiconductor layer of the TFTs is less than 1500 Å, the thermal processing greatly promotes growth of the silicide, leading to deterioration of the characteristics of the TFTs.